The phenolic resin provides a molding excellent in mechanical properties, and hence has widely been employed from of old either independently or in the form of a blend with another resin, such as an epoxy resin. However, the phenolic resin per se and blend thereof have drawbacks in that the light and alkali resistances are relatively low, that they are likely to absorb water or an alcohol to thereby suffer from changes in the dimension and electrical resistance, and that the thermal resistance, especially the oxidation resistance at high temperatures, thereof is poor.
In order to overcome the drawbacks, various modifications of the phenolic resin have been studied. For example, various modified phenolic resins have been proposed, which have improved resistances to deterioration and oxidation due to light, chemicals, etc. by virtue of the modification using fats and fatty oils, a rosin or a neutral aromatic compound.
Among the various proposals, Japanese Patent Application Laid-Open Publication No. 235413/1986 discloses a preparation of a phenol-modified aromatic hydrocarbon resin having excellent thermal resistance by selecting reactants thereof. However, the phenolic resin obtained by this method is disadvantageously not cured unless being maintained at a high temperature for a prolonged period of time in the manufacturing of a molding by the use thereof.
Japanese Patent Application Laid-Open Publication No. 274714/1990 discloses that a modified phenolic resin useful as a molding material, having excellent thermal and oxidation resistances and mechanical strength as cannot be expected from the conventional phenolic resin, is obtained by employing a petroleum heavy oil or a petroleum pitch, which is a cheap material, as a modifier material and by selecting specific reaction conditions.
Further, Japanese Patent Application Laid-Open Publication No. 145116/1992 discloses that, in the production of such a phenolic resin, a crude modified phenolic resin obtained by a polycondensation of starting compounds may be subjected to a neutralization treatment, a water washing treatment and/or an extraction treatment to thereby neutralize and remove any acid remaining in the crude modified phenolic resin, so that a modified phenolic resin which does not corrode a metal member in contact with the resin is provided.
In the above process for producing the modified phenolic resin, the acid remaining in the crude modified phenolic resin is actually neutralized and removed by the neutralization treatment using an amine, followed by the water washing treatment. However, the modified phenolic resin obtained through the purification step comprising the above neutralization and water washing treatments is likely to retain a neutralization product, so that there is a problem that it is unsatisfactory as a molding material for a product on which strict requirements for thermal and corrosion resistances are imposed, such as a molding material for an electrical or electronic part and a material for a semiconductor sealer.
In the above situation of the prior art, the inventors have made extensive and intensive studies. As a result, it has unexpectedly been found that a modified phenolic resin containing substantially no acid can be provided by purifying a crude modified phenolic resin obtained by polycondensation of starting compounds through a purification step comprising a characteristic extraction treatment.
Moreover, the inventors have found that a molding material based on a modified phenolic resin, which provides a molding having excellent thermal, moisture and corrosion resistances, can be obtained by the employment of the specific modified phenolic resin containing substantially no acid in combination with an epoxy resin. Based on these findings, the present invention has been completed.